Cathode-ray apparatus



. 24, 1946. wLFF CATHODE RAY APPARATUS 2 Sheets-Sheet l Filed Nov. 19, 1942 iugm INVENTOR Wmo? ATTORNEY Dec. 24, 1946. l. woLFF CATHODE RAY APPARATUS Filed Nov. 19, 1942 2 sheets-sheet 2 TTORNEY Patented Dec. 24, 1946 naar tries oATHoDE-RAY APPARATUS Irving Wol, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Dela- Walle Application November 19, 1942, Serial No. 466,129

12 Claims.

My invention relates to improvements in cathode ray tubes and apparatus and particularly to tubes and apparatus and methods for developing a curvilinear or circular time base utilized for indicating electrical phenomena.

It has been proposed in the prior art to utilize a cathode ray tubehaving a target screen for measurements or for picture transmission wherein the time base is evidenced by a closed curved trace either on a luminescent screen as shown by Heymann, 2,200,745, or on a target of the mosaic type as shown by Hickok, 2,272,842. Tubes hav ing luminescent screens wherein the cathode ray beam is deflected to form a closed curved trace, such as a circle on the screen, have particular application in radio position and distance indicating equipment wherein the distance or position is indicated by a radial deflection of the beam from the normally produced circular trace. It has been customary'to form such curved closed traces utilizing quadrature deflection. For eX- ample, two mutually perpendicular'pairs of deilection plates are supplied with sine-wave potentials, one of which is in quadrature with the other. Such arrangements are not as iiexible as desired and inv addition require rather critical adjustment to maintain theV quadrature relationship.

Among the objects of my invention are: to provide apparatus for and a method of producing a curved time base for cathode ray beam deilection, to provide means for obtaining curved time bases for cathode ray deiiection without recourse to phase delay or quadrature networks, to provide apparatus wherein circular time base deflection may be obtained without recourse to critically adjusted circuits, to provide a highly stable tube inherently capable of producing closed deection traces having uniform curvature to provide a curved time axis in which substantially any relationship may exist between angular position and time, and to provide a method and means whereby a spiral time axis may be obtained. These and other objects, features, and advantages of my invention will become evident upon consideration of the following description and the accompanying drawings wherein:

Figure 1 shows cathode ray apparatus, in sectional plan view, made and operated in accordance with my invention; and

Figure 2 is a perspective View, partially in section, of a greatly simplified embodiment of my invention. Y

As indicated above, it is diificult to provide closed curved traces in cathode ray tubes because of the necessity of producing quadrature deflection potentials which for circular traces must be matched both as to quadrature relationship and potential variations. Thus a change in frequency in the applied quadrature deflection potentials requires a change in the circuits developing these potentials. In addition, the potentials forsuch deflection must be relatively high especially in tubesY operating at relatively high voltage, to obtain an intense trace on a luminescent screen. Such high potentials necessitate extensive equipment which is not only bulky but necessitates an increase in the weight factor wherefsuch apparatus is utilized in aircraft applications. y

In accordance with kmy invention I obtain a curved deflection trace in a cathode ray tube by directing an electron beam into an axial magnetic or radial electrostatic vfield at an angle to the axis and with its projection tangent toa circle about the axis'of the field. I deflect the beam to vary the angle of entrance into the-field to control and vary the pitch of the helical path of the beam. More particularly, I have found that the degree of angular deflection imparted to the beam is inversely proportional to the angle the beam makes with a plane perpendicular to the axis of the field. Still further, I direct the electron beam through the field thereby imparting an eifective rotation to the beam and I'so limit the field in length that the beam emerges from the eld and continues in adirection determined by the angle of entrance into the field and I then intercept the beam by a target, such as of the luminescent type, to provide the curved time base. Following emergence from the field the electron beam may be given further radial deilection, such as a signal deflection, to produce indications of the phenomena to be observed.

The foregoing description of the principles of my invention will be more readily appreciated by references to Figure 1 wherein the apparatus or tube per se comprises an elongated envelopedy having a neck portion 3 and a frusto-conical portion 5 which is provided at its closed end with a luminescent screen l. The electron beam is developed by an electron gun preferably disposed to direct the-beam at an angle to the longitudinal axis of the envelope portions 3 and 5 and to one side thereof and comprises the conventional cathode 9, control electrode Il'connected'to the usual biasing source, a first anode I3 and a second anode l5 so that the developed electron beam in an undeflected position is directed preferably perpendicularly to a radius of a circle surrounding the axis andY at an angle to a plane normal to said longitudinal axis. The electron beam may be grid modulated to vary the beam intensity such as by applying potential variations across the terminals il, the shunt i9 shown in dashed lines being provided when no modulation is applied. The electron beam is developed by applying potentials between the cathode and the first and second anodes, such as by a battery or potential source 2! provided with a bleeder 23. Situated on either side of the electron gun axis I provide means to deflect the electron beam such that the rate of travel along said longitudinal axis de pends upon the degree of deflection. Such deflection means may comprise a pair of deflection plates ESL-2l although magnetic deiiection means may be provided in lieu thereof.

g In accordance with my invention I direct the deflected beam into a longitudinal axial field such as a magnetic iield of relatively long extent or length developed by a coil 29 enclosing the principal portion of the neck section 3 between the intersection of the electron gun envelope portion and extending in the direction of the target or screen 1. The beam upon entering this magnetic eld will follow helical paths over an extent determined by the angle of incidence between the entering beam and the longitudinal magnetic field so that the beam will follow a helical path throughout the length of the field. Upon termination of the helical path, the electron beam conn tinues to the screen 'l along unconstrained paths and impinges the screen at a position determined by the original deflection such as by the plates 25-21. Since the electron beam enters the field at these different angles and follows a path whose extent is determined by this incident angle, the beam emerges at various points lying on a circle, the beam then continuing along diverging paths to the screen l. The dashed lines show representative beam paths for the 180 degrees of defiection by the plates 25--2l- The electron beam may be developed and deected at relatively low potentials and further accelerated along the length of the envelope portions 3 and 5 by a series of electrodes surrounding the beam. For example, the electrodes 3 l-3'l may bein the form of electrically conductive coatings positioned in the order named in a direction from the electron gun to the screen and may be supplied with operating potentials from the potential bleeder 23. Further electrodes of similar formation, such as the electrodes 39 and lll, may be provided along the frusto-conical portion E and may likewise be operated from the potential source 2l or bleeder 23. While I have shown these electrodes as progressively more positive in the direction of the screen, it will be appreciated that depending upon the length and diameter of these electrodes the potentials applied thereto will vary with differ ent constructions although the final electrode or electrodes such as 3B and il are preferably operm ated at high positive potentialsl with respect to deilection potentials, such as representative of signal deection, may be applied with respect to the surrounding electrode i l. Thus the electrodes 4! and 43 provide a concentric system which defleets the electron beam radially from the curved path or trace to provide an indication of the fre- 4 quency, timing, and amplitude of the applied signal.

It should be particularly noted that the voltage applied to the deflecting plates 25-21 may be of any desired time function and that the rate of angular deflection will approximately follow the same time function. To obtain uniform circular sweep a linear sawtooth deection of amplitude sufcient for one rotation may be used. However, if it is desirable to spread any part of the scale, an exponential or other type of sweep having nonuniform voltage change may be employed. Blanking circuits whose construction is well known in the art may be used to eliminate the effect of the return line by 4developing blanking signals which are applied across the terminals il. A spiral type of indication either with uniform or nonuniform angular velocity may also readily be obtained with my tube. This result may be accom plished by imposing some of the sweep deflecting voltage between the central radial deflecting electrode 39 and the electrode l l. A fixed radial electrostatic field may be used in place of the longitudinal magnetic iield in order to supply the radial force to cause the electrons to assume spiral paths. However, in general the longitudinal magnetic field is to be preferred because of better focusing action.

A better understanding of the motion and trajectory of the electron beam may be obtained by reference to Figure 2 wherein an envelope encloses an electron gun 4 and target structure 8. In contradistinction to the previously described tube the electron gun 4 is located within the longitudinal field developed by the coil no deflection being imparted to the beam since this showing is merely for purposes of explanation. I position the electron gun 4 to emit the electrons in a 'direction at an angle to the axial magnetic field and tangential to a circle about the axial magnetic eld. Only one beam path is shown since no deflection of the beam is provided. Thus the dashed line in Figure 2 represents the beam motion along a helical trajectory intercepting the target 6 at the point IB, this helical path being of uniform diameter and pitch. It will be noted that the projection of the beam paths on a plane normal to the eld axis is always, tangentto the beam path as it leaves the electron gun. However, assuming that the location of the electron gun 4 is moved so that the beam is initiated at a dilferent angle to a plane normal to the longitudinal axial field, the radial 4deflection will be different from that shown kand the point at which the beam intercepts the target will be displaced from the point lll such as to the point l2. The movement of the electron gun to initiate the beam at different angles to this plane is thus equivalent to deflecting the beam by the plates 25-21 in Figure 1 thereby causing the beam to describe a path on the screen 'l as modified by radial den ilection components applied between the electrodes 4I-43.

The amplitude, that is the diameter, oi the trace may be controlled by varying the ratio between the field strength, such as the magnetic field delevoped by the coil 2@ and the potential applied to the various electrodes determinative of the electron beam velocity while the beam is under the influence of the magneticeld. For example, the stronger the magnetic field develcned by the coil 253, the smaller will be the diameter of the trace developedppon the screen 'l for a given beam velocity. Similarly, the lower the velocity ,of the beam while under the influence of the magnetic field, the smaller will be the diameter of the beam trace on the screen 1 for a given magnetic field strength. Consequently, the diameter of the trace may be adjusted within the spatial limits of the screen by controlling the ratio of the field strength to beam velocity. Preferably, the magnetic eld strength is of the order of 50 to 100 gausses, being relatively strong to minimize eiects produced by extraneous magnetic fields. Furthermore, for particular constructions it may be found that the fringe portion of the field developed by the coil 29 interacts in the electron gun or deflection space so that magnetic shielding means such as a slotted shield 45 may be provided between the deection plates -21 and the magnetic coil 29. The effect of the shield may be extended by an external shield as shown at 6l, the need for such shielding arrangements being determined by the distance between the deflection plates 25--21 and the coil 29.

It will be appreciated that my method of electron beam deflection is not dependent upon the specific apparatus disclosed above, but that the method may be practiced entirely by hand. For example, an electron beam developed in any manner may be deflected by hand such as by manually moving the electron gun through an angle in a predetermined plane, developing a magnetic field such as forming a eld between apertured pole faces to develop the helical motion of the beam, radially deflecting the beam by manually manipulating an electrostatic element following emergence of the beam from the longitudinal magnetic field and intercepting the beam to render it manifest.

While I have described my invention with particular references to its use in tubes of the luminescent screen type, it will be appreciated that its application is not so limited, the principles and advantages of my invention accruing equally to tubes of the television transmitting type shown by the above-mentioned Hickok patent. In addition, while I have described my invention particularly with respect to an axial magnetic eld, it will be appreciated that an axial electrostatic eld may be used substantially with equal advantage. Such a eld may be developed between two concentric cylindrical electrodes maintained at different potentials and extending over the space occupied by the magnetic coil 29 so that the electron beam is directed into the eld in a direction at an angle to the axis of the equipotential lines of the field and with its pro` jection tangent to a circle about the axis of the field. Furthermore, while I have described only two particular embodiments of my invention, it will be appreciated that many variations thereof will occur to those skilled in the art and that my invention is not limited to the specic apparatus shown or its mode of operation except as set forth in the appended claims.

I claim:

l. The method of defiecting an electron beam over a target surface comprising sweeping the beam in a plane through a predetermined angle, developing an axial magnetic field having lines of force in said plane but at an angle to said beam and to one side of the centrally .disposed axis of said eld to cause said beam to follow helical paths, and intercepting said beam with a target surface.

2. The method of deflecting an electron beam over a target surface comprising developing an axial field having lines of force extending substantially parallel to and surrounding a longitudinal axis, developing an electron beam, directing said beam into said field in a direction at an angle to the said axis and tangentially to a right circular1 cylindrical surface surrounding said axis, varying said angle at which said beam intercepts said eld to cause said beam to follow helical paths, and intercepting said beam with a target surface.

3. Cathode ray apparatus comprising an evacuated envelope, a target within said envelope adapted to be impinged by an electron beam approaching said target substantially about an axis normal thereto, electron beam forming means within said envelope positioned to direct an electron beam along an undeflected path at an angle to the said axis, field means for establishing a eld of force extending along said axis for rotating said electron beam around said'longitudinal and means adjacent said electron gun for directing the electron beam at a varying angle to said longitudinal axis in a plane parallel thereto and including said undeilected electron beam path.

4. Cathode ray apparatus comprising an elongated evacuated envelope, a target near one end of said envelope adapted to be impinged by an electron beam, electron beam forming means near the opposite end of said envelope positioned with its axis at an angle to the longitudinal axis of said envelope, eld means for establishing a field of force` for rotating said electron beam around said longitudinal axis, and means adjacent said electron gun for directing the electron beam at a varying angle to said longitudinal axis in a single plane parallel thereto and including said electron beam. v

5. Cathode ray apparatus comprising an evacuated envelope, a target near one end of and transverse to an axis extending within said envelope adapted to be impinged by an electron beam, electron beam forming means near the opposite end of said envelope positioned to direct an electron beam along a path at an angle to and offset from the said axis, means for establishing a magnetic field having lines parallel to and surrounding said axis for rotating said electron beam in a helical path around said axis, and means adjacent said electron gun for directing the electron beam at a varying angle to said longitudinal axis in a plane parallel thereto and including said electron beam path.

6. Cathode ray apparatus comprising an elongated envelope, a target adjacent one end of said envelope, an electron gun adjacent the opposite end of said envelope positioned to develop and direct an electron beam at an angle to and offset from said longitudinal axis, means adjacent said gun and said longitudinal axis to deilect the beam in a plane parallel to said axis and magnetic means to develop a longitudinal magnetic iield extending from the point of intersection most remote from said target and in a direction toward said screen, parallel to said plane, and surrounding said axis to direct said beam toward said target along helical paths.

7. Cathode ray apparatus comprising an evacuated envelope, a luminescent target adjacen't one end -and intercepting a Alongitudinal axis Within said envelope, an electron gun including a plurality of apertured anodes with the apertures aligned along a line disposed at an acute angle to the longitudinal axis of said envelope to develop and direct an electron beam in a plane parallel to said longitudinal axis, de-

flection means to shift the direction of said beam in said plane, magnetic means to develop a longitudinal magnetic field substantially parallel with said axis and intercepting the plane of deection of said beam to sweep said beam in combination with said deection means over a curved path on said target and a pair of telescoped concentric electrodes between said magnetic means and said target to deflect said beam in a direction radially of said longitudinal axis.

8. Cathode ray apparatus comprising an evacuated envelope, a luminescent screen positioned transversely of and at one end of said envelope, an electron gun at the opposite end of said envelope positioned to develop and direct an electron beam alongV an initial path at an angle to said screen, an elongated magnetic field developing coil positioned with its longitudinal axis substantially normal to said screen and at an angle to the initial path of Said beam to develop a magnetic iield in the path of said beam, a pair of oppositely disposed deflection plates, one on either side of the undeected path of said beam and adjacent said electron gun to deflect the electron beam in a plane parallel to and offset from the axis of said magnetic coil, and a pair of concentric telescoping electrodes along said axis and closely adjacent said screen to radially deect said electron beam from the path on said screen determined by the angle of deection in said plane.

9. Cathode ray apparatus comprising an evacuated envelope, a luminescent screen at one end of said envelope, an electron gun at the oppo site end of said envelope positioned to develop and direct an electron beam along an undeiiected path not intercepted by said screen, a magnetic eld generating coil surrounding a portion of said envelope and positioned to develop a eld having lines of force at an angle to and intercepting the undeected path of said beam, electrode means in the region of said magnetic iield to direct electrons in combination with said eld along a helical path toward and upon said therebetween positioned Without the magnetic eld developed by said coil and closely adjacent said luminescent screen to radially deflect said electron beam from said curved trace.

10. The steps in the method which comprises, producing a eld, projecting an electron beam into said eld at an angle to the lines of force Y thereof, and causing the electrons of the beam to travel in a helical path through said field and cyclically varying said angle'to vary the path and cause the electron beam to pass through a plane at a multiplicity of points of a continuous curve around the axis of said field.

11. The steps in the method which comprises, producing a constant eld, projecting an electron beam into said eld at an angle to the lines of force thereof, and causing the electrons of the beam to travel in a helical path through said field and cyclically varying said angle to vary the path, and cause the electron beam to emerge from the iield at a multiplicity of substantially contiguous points of a circle having its centerV in the axis of said eld.

12. 'I'he method of producing a circular trace on a target which comprises, producing a constant field, projecting an electron beam into said eld at an angle to the lines of force thereof, and causing the electrons of the beam to travel in a helical path through said iield, cyclically varying said angle to vary the path and cause the electron beam to emerge from the eld at a multiplicity of substantially contiguous points of a circle having its center in the axis of said eld, and causing the emerged ray to Strike said target.

IRVING WOLFF. 

